When producing hydrocarbon-containing fluid from a reservoir from different production zones, the inflow of fluid is adjusted if e.g. a production zone is producing too much water or the pressure in one zone is much lower than a pressure in another zone. Such adjustment is mainly performed by submerging a tool into the well, and when the tool is opposite the inflow valve to be adjusted, the tool engages the valve and opens or closes the valve. Another way of adjusting the inflow is to have control lines on the outside of the metal casing, so that the valves can be adjusted from surface.
Adjusting the valves by submerging a tool into the well takes time, and adjusting the valves through control lines or flow lines jeopardises the well safety as the lines are to run through the main barriers at the top of the well, inducing the potential risk of a leak and thus of a blow-out. Therefore, attempts have been made to design autonomous valves, e.g. having swellable elements reacting to water or valves lowering the pressure of the fluid using a vortex principle if the water content of the fluid is too high. However, none of these autonomous valves is sufficiently reliable, as they do not always function as intended, and the adjustment of some of the valves is irreversible.